A polymer having a silsesquioxane skeleton has been investigated for various applications owing to the peculiar structure thereof. A polymer having a silsesquioxane skeleton has been synthesized by the sol-gel process using an alkoxysilane, such as tetraethoxysilane. However, the sol-gel process has some remaining problems in that it requires prolonged reaction time, and a resulting polymer tends to have fine pores remaining therein.
A polymer using a silsesquioxane having a cage structure or a derivative thereof has been investigated. The polymer is expected to be excellent in weather resistance, heat resistance, physical properties, optical properties and the like. For example, Patent Documents 1 and 2 disclose a production process of a copolymer obtained by bonding a so-called incomplete cage structures, which has a defect in the cage structure of silsesquioxane (i.e., a structure not having a complete octahedral shape but having a defect in the octahedral shape), through siloxane. The production process uses such a method that a polyhedral oligomeric silsesquioxane is crosslinked through a bifunctional silane having an amine or the like as a functional group, siloxane or an organic metal compound. Non-patent Document 1 discloses a production process of a copolymer having a main chain obtained by bonding a silsesquioxane having an incomplete cage structure through siloxane or the like, and a production process of a copolymer having a silsesquioxane having a cage structure as a pendant copolymer component and methacrylic acid as a main chain component. Furthermore, Non-patent Document 2 discloses a production process of a silsesquioxane-siloxane copolymer obtained by reacting OH bonded to Si positioned at a corner of an incomplete cage structure of silsesquioxane with bis(dimethylamino)silane or the like.
Patent Document 3 discloses, on the other hand, a production process of a copolymer by reacting a silsesquioxane having a complete cage structure with a compound having a vinyl group. Non-patent Document 3 reports that hydrogenated octasilsesquioxane and phenylethynylbenzene are subjected to hydrosilylation polymerization to obtain a copolymer. Non-patent Document 4 reports that a silsesquioxane compound having a complete cage structure with vinyl groups bonded to plural corners of the cage structure and a hydrogenated silsesquioxane compound having a complete cage structure are subjected to hydrosilylation polymerization to obtain a gelled copolymer. Patent Documents 4 and 5 disclose a production process for obtaining a copolymer having an organic solvent soluble hydrogenated octasilsesquioxane by a reaction of a hydrogenated octasilsesquioxane having a cage structure with a hydroxyl group-containing compound or a vinyl group-containing compound. All of these have such a structure that a silsesquioxane having a complete cage structure is grafted to a main chain or forms a crosslinked point. In the case where a silsesquioxane having a cage structure is grafted to a polymer chain, the silsesquioxane exhibits a modification effect to the polymer by inhibiting the local molecular motion, but does not contribute to change in polymer chain structure. In the case where a silsesquioxane forms a crosslinked point, on the other hand, a gelled copolymer is formed, which is inferior in moldability.
Patent Document 1: U.S. Pat. No. 5,412,053
Patent Document 2: U.S. Pat. No. 5,589,562
Patent Document 3: U.S. Pat. No. 5,484,867
Patent Document 4: JP-A-2002-069191
Patent Document 5: JP-A-2000-265065
Non-patent Document 1: Comments Inorg. Chem., vol. 17, pp. 115-130 (1995)
Non-patent Document 2: Macromolecules, vol. 26, pp. 2141-2142 (1993)
Non-patent Document 3: Chem. Lett., 1998, pp. 763-764
Non-patent Document 4: J. Am. Chem. Soc., vol. 120, pp. 8380-8391 (1998)
Non-patent Document 5: Polymer Preprints, Japan, vol. 50, No. 12 (2001)
In electric and electronic materials, particularly, insulating property, heat resistance, durability, moldability and the like thereof are demanded to be further improved. However, the conventional silsesquioxane polymers fail to satisfy the properties. Accordingly, such a copolymer has been demanded that has a silsesquioxane having a cage structure excellent in heat resistance, weather resistance, electric insulating property, hardness, mechanical strength, chemical resistance and the like as a main chain, is clearly defined in position of bond, and is excellent in moldability. However, a copolymer having a silsesquioxane having a cage structure as a main chain is difficult to produce by using conventional compounds. Non-patent Document 5 discloses compounds capable of being used as a raw material of the main chain type polymer, but there is only one disclosed example for a copolymer having a silsesquioxane skeleton of a T8 structure introduced into a main chain, and specific characteristics thereof are not sufficiently clarified. Furthermore, the copolymer still has room for improvement, e.g., it has a glass transition temperature of 125° C. By introducing a silsesquioxane skeleton having a T8D2 structure or a structure similar thereto into a main chain, the molecular weight or the like can be arbitrarily controlled to adjust the physical properties to intended values. Assuming that a structure where three oxygens are bonded to Si is referred to as a T structure, and a structure where two oxygens are bonded to Si is referred to as a D structure, the T8D2 structure means such a structure that is formed by combining eight T structures and two D structures.